Field of the Invention
The present invention relates to a configuration for testing chips, i.e., integrated circuits realized in the chips, using a printed circuit board (xe2x80x9cPCBxe2x80x9d), in which an electrical connection is produced between the PCB and the chip by probe needles.
Chip testing is preferably performed at the wafer level because a multiplicity of chips can be processed in parallel at that level. As such, considerable time and cost is saved. Particularly highly parallel contact-making methods that are based on small dimensioned needles and that take account of a form factor, for example, have recently been regarded as promising. Such tests can, in principle, be carried out by two different methods.
In a first method, a number of highly accurate probe needles are provided on each chip. The probe needles are brought into contact with pads or contact pads on a PCB.
In a second method, the probe needles are fitted in large numbers on a probe card that is used for the parallel testing of a plurality of chips.
The first and second methods are illustrated in FIGS. 2 and 3, respectively.
In FIG. 2, chips 1, 2 are each provided with probe needles 3 that are brought into contact with pads 4 on a PCB 5.
In contrast, the second method uses a probe card 6 equipped with a multiplicity of such probe needles 3 that are brought into contact with a multiplicity of chips 1 on a silicon semiconductor wafer 7.
The first method allows parallel testing of the individual chips 1, 2 on the PCB 5. In the first method, care has to be taken to ensure that the probe needles 3 respectively meet and make reliable contact with their assigned pads 4. A disadvantage of the first method is that accurate centering of the individual probe needles on the pads is difficult, and that the probe needles have to be fixedly connected to the individual chips. Such fixation renders further processing more difficult because the probe needles cannot be removed practically. As a result, the needles have to be taken into account during further use of the chips. In addition, realizing a complete set of probe needles for each chip constitutes a considerable expenditure.
The second method using a probe card 6 does not have the disadvantage of a high outlay for probe needles for each chip. The probe card, with its probe needles, can successively make contact with different sets of chips or the pads thereof. However, the probe card method does have a disadvantage that making contact with the chips of an entire semiconductor wafer is practically ruled out because, according to the current prior art, it is not possible to realize probe cards having tens of thousands of individual probe needles. Such a configuration is necessary because a semiconductor wafer can have up to 1000 chips, with approximately 60 probe needles required for each of these chips. Accordingly, 60,000 probe needles, in total, are necessary for a probe card that tests a wafer or the chips in the wafer. Moreover, it self-evident that working with such a large number of probe needles requires extremely high accuracy in the lateral and perpendicular directions, i.e., in the plane of the semiconductor wafer and in the direction perpendicular to the plane.
It is accordingly an object of the invention to provide a configuration for testing chips using a printed circuit board that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that allows parallel testing of a large number of chips with self-alignment.
The object is achieved according to the invention by virtue of the fact that the probe needles are fitted directly on the PCB, which is configured closely to the application, such that a plurality of chips can be tested in parallel on the PCB.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a configuration for testing chips, including a printed circuit board having conductive probe needles to electrically connect the printed circuit board to chips and for testing the chips on the printed circuit board in parallel, some of the probe needles configured as dummy needles for mechanically self-aligning the chips.
The invention makes a fundamental departure from the previous prior art, in that the probe needles are no longer provided on the chip, as in the first method described above, and are, likewise, no longer provided on the probe card, as in the second method described above. Rather, the probe needles are fitted directly on the PCB, resulting in the elimination of the requirements for a probe card to have the largest possible number of probe needles or for probe needles to be on the individual semiconductor chips. The PCB itself should be realized as closely as possible to the application and, for example, simulate the later use of memory chips on a Dual Inline Memory Module (xe2x80x9cDIMMxe2x80x9d).
Fitting the probe needles directly on the PCB makes it possible to make contact with and test a large number of individual chips in parallel. A DIMM-like PCB is advantageously used for testing memory chips because such a PCB allows the memory chip to be tested under application conditions.
It is particularly advantageous if dummy needles are additionally fitted on the PCB for mechanical self-alignment of the chips. These dummy needles can then engage in markings with their free ends remote from the PCB, which markings may be depressions provided on an adapter or xe2x80x9cinterposerxe2x80x9d connected to the chip. Such an interposer may be made of plastic or plastic and metal and is fixedly connected to the actual chip.
In accordance with another feature of the invention, the chips have markings and the dummy needles have free ends remote from the printed circuit board to engage the markings.
In accordance with a further feature of the invention, the markings are depressions.
In accordance with an added feature of the invention, there are provided adapters disposed between the probe needles and the chips.
In accordance with an additional feature of the invention, the chips each have a surface and structures disposed on the surface between the probe needles and respective chips.
In accordance with a concomitant feature of the invention, the printed circuit board has alignment aids for orienting the chips.
An essential advantage of the invention can be seen in the fact that, in contrast to the prior art according to the first method above, the probe needles are no longer connected to the individual chips. Thus, a significantly smaller amount of needles are necessary overall because the needles fitted on the PCB can be readily used for testing succeeding chips. In contrast to the second method described above, such high demands on accuracy, as in the case of probe cards, do not have to be imposed for the configuration according to the invention because self-centering can be achieved by the dummy needles. These dummy needles ensure correct alignment of the probe needles on the pads of the chip or interposer.
The configuration according to the invention also allows testing under similar conditions to those in an actual application of the chips. As a result, it is possible to dispense with safety margins during tests because defective chips can be reliably screened out.
Finally, a further advantage of the configuration according to the invention is that (in contrast to the first method described above) it is possible to dispense with complicated and precise fitting of holders or sockets on the PCB that are often necessary instead of pads.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration for testing chips using a printed circuit board, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.